Wladimir Klitschko, born 25 March 1976, is a Ukrainian former professional boxer who competed from 1996 to 2017. He held the world heavyweight championship twice, including the unified WBA (Super), IBF, WBO, IBO, and Ring magazine titles. A strategic and intelligent boxer, Klitschko is considered to be one of the greatest heavyweight champions of all time. He was known for his exceptional knockout power, using a strong jab, straight right hand and left hook, quick hand speed, great physical strength which he employed when clinching opponents, and his athletic footwork and mobility, unusual for boxers of his size.

During Klitschko's reign as world heavyweight champion, his fights regularly generated a global television audience of 300–500 million viewers. Klitschko holds records for the longest cumulative heavyweight title reign of all time, with 4,382 days as world heavyweight champion, and most fighters beaten for the world heavyweight championship, at 23. He also holds records for the most wins and title defences of the unified championship in professional boxing history. In 2011, both Wladimir and Vitali entered the Guinness World Records book as brothers with most world heavyweight title fight wins (30 at the time; 40 as of 2020). Klitschko was inducted into the International Boxing Hall of Fame Class of 2021, having been elected in his first year of eligibility.